Moulded Cog or Raw-edge V-belts have higher capacity and efficiency and they use smaller pulleys than traditional envelope (wrapped) belts. These belts have a higher coefficient of friction and are more aggressive, which makes them a very efficient belt for power transmission Unlike conventional fabric-covered V-belts, raw-edge belts have no cover. Thus, the cross-sectional area normally occupied by the cover is used for more load-carrying cord. Cogs on the inner surface of the belt increase air flow to enhance cooler running. They also increase flexibility, allowing the belt to operate with smaller pulleys.